Field of the Invention
The present invention relates to an image-shake correction apparatus having a function of correcting shake caused by camera shake or vibration, and also relates to a control method of the image-shake correction apparatus.
Description of the Related Art
In recent years, a zoom lens used in an image pickup device such as a compact digital camera may be a super wide-angle zoom lens. With such a zoom lens, the amount of distortion generated depending on the field angle is increased.
When optical design is made for a photographing lens unit, correction on distortion by the photographing lens unit may be reduced for simplifying optical design, and the distortion may be electronically corrected by digital image processing.
Also, a recent camera is equipped with an image-stabilization control device that prevents image shake due to camera shake etc. The image-stabilization control device is briefly described here. Camera shake is vibration with a frequency in a range from about 1 to about 10 Hz.
To allow photographing without image shake even if camera shake occurs when a shutter is released, vibration of camera due to camera shake needs to be detected and image-shake correction mechanism needs to be moved in accordance with the detected value.
At this time, it is required to accurately detect camera vibration and correct a change in optical axis due to the shake. Theoretically, image shake is restricted if a vibration detector that obtains a detection result such as an angular velocity and a drive controller that displaces a correction lens on the basis of the arithmetic processing result are mounted.
There are various optical image-stabilization mechanisms.
For example, there is an optical image-shake correction system that removes shake from an image focused on an image pickup element by moving a shift lens, which serves as a correcting unit for correcting image shake and which moves in a plane perpendicular to the optical axis, by an image-shake correction amount.
Also, there are an image-pickup-element image-shake correction system that removes shake from an image by moving an image pickup element, which serves as a correcting unit for correcting image shake and which moves in a plane perpendicular to the optical axis; and a variable prism image-shake correction system that uses a variable prism the transmission deflection angle of which is variable.
Either system may be a subject of the present invention. Hence, a configuration of an optical image-shake correction system is representatively described below.
An image pickup device including the optical image-shake correction system performs image-shake correction by instructing a shift lens driver for movement by an image-shake correction amount calculated from a detection signal from a vibration detector, and driving the shift lens as a control subject to a target value.
Japanese Patent Laid-Open No. 2006-129175 discloses an image pickup device in which distortion correction and an optical image-stabilization mechanism are combined, so that enlargement and reduction in a peripheral edge portion of an image caused by optical aberration of a lens group are prevented from occurring.
With this method, if an optical image-stabilization mechanism is provided and an image pickup optical system having optical distortion remaining therein is provided, degradation in image quality caused by distortion in a peripheral portion can be reduced.
In an image pickup device including an image pickup optical system whose distortion changes in a barrel shape or a pincushion shape depending on zoom magnification, not only the lateral magnification in a peripheral portion of an image but also the lateral magnification in a center portion of the image may noticeably change.
Distortion can be corrected in accordance with characteristics previously set by lens characteristics after an image is acquired by an image pickup device. If a lens has barrel-shaped distortion as shown in FIG. 4A, a peripheral portion of an image may be reduced as compared with a center portion, and therefore the image is corrected to enlarge the peripheral portion.
Also, if a lens has pincushion-shaped distortion as shown in FIG. 4B, a center portion of an image may be reduced as compared with a peripheral portion, and therefore the image is corrected to enlarge the center portion.
However, in an optical image-stabilization mechanism built in an image pickup optical system, optical image stabilization has to be performed in image pickup optical characteristics having optical distortion remaining therein. Hence, it is difficult to properly provide optical image stabilizing effect in all region of an image.
Particularly in a general photographing scene, the resolution in a center portion of an image is emphasized the most in many cases. However, in normal optical image stabilization, correction is made to decrease shake in the entire image.
For example, in the case of an optical system having barrel-shaped distortion as shown in FIG. 4B, although image stabilization effect in a peripheral portion of an image is proper, image stabilization effect in a center portion of the image may become weak due to the influence of a change in lateral magnification in a portion near the center.
Also, there may be a scene in which a main object is not located in a portion near the center of an image. For example, the position at which a user sets an area where a main object is present or the position of a main object such as a face detected by a method such as shape analysis from image data may be largely separated from the center of an image.
In this case, the image stabilization effect at the object position should be emphasized the most. However, the shake correction effect may vary depending on the characteristics of distortion at the object position.
The present invention provides an image pickup device and an image stabilization control device that can provide stable camera shake correction effect in an image region that requires shake correction the most in an image pickup optical system having optical distortion remaining therein.